Abstract
The photoionization efficiency (PIE) spectrum of HSO was measured in the spectral range (107-130) nm by means of a discharge flow and a photoionization mass spectrometer coupled to a synchrotron as the radiation source. HSO radicals were generated by reacting O atoms with various organothiol compounds, C 2 H 5 SH, 2-C 3 H 7 SH, or HSC 2 H 4 SH, in the flow tube. The ionization energy of HSO was determined for the first time and found to be (9.918±0.016) eV. GAUSSIAN-2 calculations predict 9.897 eV for ionization to HSO + , the singlet ground state of the molecular ion, in satisfactory agreement with the experimental result. The onset to triplet HSO + may occur at (11.15±0.04) eV. A vibrational frequency of HSO + of (1150±160) cm -1 was derived from the separation of steps in the PIE spectrum. The heat of formation of HSO + was also derived and calculated to be Δ f H ° 298 ) = (228±5) kcal mol -1 . © 1997 American Institute of Physics.